U.S. Pat. No. 6,983,230 B2 discloses a method and an apparatus for determining a radiation dosage received by a product being exposed to radiation in an irradiator cell through a computer simulation. The method initiates with a point on the product being defined. Then, pre-calculated lengths between the point on the product and the radiation source at each of a set of locations in the cell are identified. Next, a dosage of radiation to be received by the point on the product at each location is calculated using the pre-calculated lengths.